1. Field of the Invention
This invention pertains generally to nebulizers for generating medicinal aerosols, and more particularly to a pneumatic nebulizing apparatus with fully scalable flow rates and output volumes which is suitable for delivering medicinal aerosol to neonates and children as well as to adults.
2. Description of the Background Art
Medical compressed-gas-operated nebulizers of various types have been widely used for inhalation delivery of aerosols containing medication or other constituents to the conductive airways of the lung and the gas exchange regions of the deep lung. Aerosols are relatively stable suspensions of finely divided droplets or solid particles in a gaseous medium, usually in air. When inhaled, aerosol particles may be deposited by contact upon the various surfaces of the respiratory tract leading to potential injury, desirable therapeutic action, or planned diagnostic behavior depending on the particular properties of the particles. Inhalable aerosols are those consisting of particles smaller than 10 micrometers in aerodynamic equivalent diameter.
Because of the high permeability of the lung and the copious blood flow, medications depositing in the lung can readily enter the blood for action throughout the body, while other medications can directly influence the airway epithelium and effect responses via various airway receptors. Properly generated and formulated aerosols can therefore be helpful in medical treatment. As tracers of airflow or indicators of lung responses, other types of aerosol particles deposited in the lung can also be a valuable diagnostic tool.
A nebulizer produces aerosols of fine particles by breaking a fluid into fine droplets and dispersing them into a flowing stream of gas. The droplet size from a medical nebulizer is considerably smaller than a conventional spray atomizer. Medical nebulizers are designed to convert water or aqueous solutions or colloidal suspensions to aerosols of fine, inhalable droplets that can enter the lungs of a patient during inhalation and deposit on the surface of the respiratory airways.
Pneumatic (compressed gas) medical nebulizers heretofore developed typically provide approximately 15 to 30 microliters of aerosol per liter of gas in finely divided droplets with volume or mass median diameters in the respirable range smaller than 4 micrometers. However, these nebulizers are optimized for treatment of adults utilizing volumetric flow rates greater than 3 liters of aerosol delivered per minute. For the treatment of children or infants, flow rates ranging from less than 1 liter per minute to approximately 3 liters per minute are desirable, since higher flow rates exceed the patient demand and cause improper treatment arrangements and considerable wasted aerosol.
Nebulizers optimized for treatment of adults are not scalable to provide for lower flow rates for use with infants and children. There is no known nebulizer available which can provide flow rates from less than 1 liter per minute to approximately 3 liters per minute when operated at normal gas pressures of approximately 103 to 343 kilopascals (15 to 50 pounds per square inch gauge pressure). As a result, it is necessary to reduce the gas pressure to use conventional nebulizers for treatment of infants and children. Doing so, however, results in incomplete nebulization of fluid and production of particles larger than 10 micrometers, which results in poor treatment of the patient.
Therefore, a need exists for a nebulizer which can provide flow rates from less than 1 liter per minute to approximately 3 liters per minute at normal gas pressures. The present invention satisfies that need and provides the further advantage of having scalable design parameters which permits any flow rate and output volume to be accommodated at normal gas pressures. By providing for high aerosol concentration and ideal particle size distribution at all flow rates, the present invention is suitable for treatment of adults, children, and infants.